In order to eliminate new pediatric HIV infections, save maternal lives, and simplify antiretroviral therapy (ART) implementation in settings with generalized HIV epidemics, current WHO guidance recommends lifelong triple ART for all pregnant and breastfeeding women (Option B+). However, despite the promise of Option B+ to remove logistical barriers and to promote maternal health through life-long ART, this strategy brings challenges. Key amongst these challenges is adherence to ART and continuous retention in HIV care, especially for women who do not require ART for their own health. Barriers to adherence and retention in care for prevention of mother-to-child transmission (PMTCT) have been identified at the individual, interpersonal, community, and health facility levels; yet specific barriers in the context of Option B+ are not well understood. Our study will b conducted at 20 health facilities and associated communities in Nyanza Province, Kenya where MTCT rates prior to Option B+ roll-out remained near 10%, despite the wide availability of PMTCT services. As Option B+ is scaled up in Kenya, it is essential to identify effective methods to ensure long-term adherence and retention in care for mother-baby pairs, throughout pregnancy, breastfeeding, and beyond. Building on our team's prior research experience in this setting, we propose to gain understanding of and address potential barriers at the individual, community, and health facility levels through formative research with HIV-positive pregnant and postpartum women, their male partners, and health care providers. This information will be used to refine two proposed interventions that are highly likely to maximize ART adherence and retention in care among HIV-infected pregnant women and HIV-exposed infants. These interventions will be rigorously tested in rural Kenya; using a cluster randomized 2x2 factorial designs. The evidence-based interventions to be tested will include 1) community Mentor Mothers (cMM) who will provide support for ART adherence and retention in care for HIV-positive women in the community and 2) individually tailored, theory- based mobile phone text messages to help retain women and infants in HIV care. Our overall goal is to determine which intervention (or combination of interventions) maximizes ART adherence and retention in care in the context of Option B+ and thus improves maternal and infant health outcomes. Our primary outcomes will include ART adherence at 12 months postpartum and retention in care, measured by a documented HIV care visit within 90 days prior to 12 months postpartum. Secondary outcomes will include MTCT at 6 weeks, 12 months and 18 months; as well as maternal viral loads and CD4 counts. Results from this study will inform the scale-up of Option B+ in Kenya by identifying effective interventions and combinations of interventions that can reduce barriers and increase facilitators of optimal ART adherence and retention in care with the aims of reaching the elimination of mother to child transmission of HIV and significantly improving maternal health.